A particularly advantageous application, although not at all limiting, of the present invention is for the reception of a BPSK (Binary Phase Shift Keying) or DBPSK (Differential BPSK) signal.
FIG. 1 schematically represents the principle for generating a BPSK signal from a binary data sequence.
As illustrated by part a) in FIG. 1, in the binary data sequence, each binary data item or “bit” can take the value 0 or 1. In the example illustrated by part a) in FIG. 1, the binary data sequence corresponds to “1 0 1 1 0 1 0”.
Part c) in FIG. 1 represents a substantially sinusoidal signal, referred to as “carrier”, and part d) in FIG. 1 represents the BPSK signal obtained by modulating the phase of the carrier by means of the binary data sequence illustrated by part a) in FIG. 1.
As illustrated by part d) in FIG. 1, when the bit to be transmitted is equal to 1, the BPSK signal is identical to the carrier. However, when the bit to be transmitted is equal to 0, the BPSK signal corresponds to the carrier phase-shifted by 180° (π), i.e. it corresponds to the carrier multiplied by a factor −1.
The BPSK signal can therefore be viewed as the product of the carrier and a sequence, illustrated by part b) in FIG. 1, of two-state symbols: a first state equal to 1 when the bit to be transmitted is equal to 1, and a second state equal to −1 when the bit to be transmitted is equal to 0.
To receive a BPSK signal, the received BPSK signal must be multiplied by a sinusoidal signal synchronized in frequency and in phase with the carrier of said BPSK signal. The result of this multiplication is then low-pass filtered before extracting the binary data sequence.
In the context of the “Internet of Things” (IoT), each everyday object is intended to become a communicating object, and is to that end equipped with a terminal suitable for transmitting data to an access network, generally over a radio link. The access network includes base stations which collect the data transmitted by said terminals.
In such a context, it is important to have solutions which are both low-cost (and therefore low-complexity) and at the same time low energy consumers. This means that, for example, many everyday objects can be made communicating without impacting their production cost significantly, and especially without impacting too much their autonomy when they are battery-operated. At the terminal end, the use of, for example, BPSK modulation provides for a simple and inexpensive solution to implement for the data transmission part.
Just as for any wireless communication system, it is important to have a large geographic coverage in order to be able to collect data transmitted by a maximum number of terminals. Although wireless communication systems for the IoT provide for a larger range than mobile telephony cellular wireless communication systems, the coverage in certain areas, in particular areas that are underground or inside buildings, remains a problem.
To address these gaps in coverage, it is appropriate to densify the access network by the addition of base stations referred to as “femtocells” which are intended to cover areas that are restricted in size and poorly served by the other base stations of the access network.
It is clear that such a densification approach must rely on particularly low-cost solutions without which the profitability of the rollouts would be compromised. In such a context, the use of the conventional BPSK demodulator, which needs to generate a sinusoidal signal that is synchronized in phase and in frequency with the carrier of the BPSK signal, turns out to be too complex and costly to implement.
In a wireless communication system for the IoT, the exchanges of data are mainly unidirectional, in this case over an uplink between the terminals and the access network. Such an operating mode is completely satisfactory for a number of applications, such as for example the remote reading of gas, water and electricity meters, the remote monitoring of buildings or houses, etc.
In some applications, it can be advantageous to also be able to perform data exchanges in the other direction, i.e. over a downlink from the access network to the terminals, for example to reconfigure a terminal and/or control an actuator linked to said terminal. However, such capability must be provided while limiting the impact on complexity, cost and electrical consumption of the terminals, such that use of the conventional BPSK demodulator is a priori ruled out.
A DBPSK signal demodulator is known from the scientific publication “A 400 MHz D-BPSK receiver with a reference-less dynamic phase-to-amplitude demodulation technique”, written by Yi-Li Tsai et al.
In this scientific publication, the demodulator includes as input a PM/AM (Phase Modulation/Amplitude Modulation) converter which converts a phase-modulated signal PM (the DBPSK signal) into an amplitude-modulated signal AM, which is introduced in the form of a digitally controlled oscillator (DCO). After having performed this PM/AM conversion on the DBPSK signal, it is possible to implement conventional AM demodulation techniques.
However, such a demodulator for DBPSK signals also turns out to be too complex and too costly to implement in a wireless communication system for the IoT.